1. Field of the Invention
The present invention relates to a magnetic recording medium such as a magnetic tape and a magnetic disc and in particular to a magnetic recording medium produced by way of layered painting and a production method thereof.
2. Description of Prior Art
Conventionally, as a video tape, audio tape, magnetic disc, and the like, a so-called paint type magnetic recording medium is widely used which is prepared by applying on a non-magnetic support body a magnetic paint prepared by dispersing in a binder a ferromagnetic powder such as a ferromagnetic iron oxide, Co-denatured iron oxide, CrO.sub.2, and the like.
Recently, in the field of magnetic recording, there has been made a great advance in the recording density and wavelength shortening. The aforementioned paint-type magnetic recording medium should also have characteristics to answer such a recording density and short wavelength.
Here, as a method to improve the electromagnetic conversion characteristic in a high density recording region on the paint-type magnetoelectric medium, there can be exemplified reduction of the thickness of a magnetic layer. When the magnetic layer is made thin, it is possible to reduce the self demagnetization loss during a recording and a thickness loss during a reproduction, effectively improving the electromagnetic characteristic.
However, if the thickness of the magnetic layer is made as thin as 2 .mu.m or below, for example, the surface configuration of a non-magnetic support body easily appears on the surface of the magnetic layer, deteriorating the surface of the magnetic layer.
To cope with this, there has been proposed a double paint type configuration of magnetic recording medium in which a lower non-magnetic layer having a comparatively large thickness is provided between the magnetic layer and the non-magnetic support body, so that the surface configuration of the non-magnetic support body cannot clearly appear on the surface of the magnetic layer. In this double paint type magnetic recording medium, it is possible to form a thin magnetic layer with a flat and smooth surface, which in turn enables to obtain an excellent electromagnetic conversion characteristic in the short wavelength region.
However, in this double paint type magnetic recording medium, there is still a problem to improve the composition and preparation method of the lower pain.
For example, in this double paint type magnetic recording medium, although it is possible to obscure the surface configuration of the non-magnetic support body appearing on the magnetic layer surface, the smoothness of the magnetic layer surface may be deteriorated depending on the preparation method of the lower non-magnetic paint. For this, in order to obtain a smooth magnetic layer surface, the composition and preparation conditions of the lower non-magnetic paint become very import but there has not been found an appropriate composition or preparation condition for this.
Moreover, in such a pint-type magnetic recording medium, in order to assure the tape running efficiency, a fatty acid lubricant is added to a magnetic paint but it is impossible to contain a sufficient amount of lubricant in the magnetic layer because the magnetic layer has a small thickness. For this, a method often used adds a fatty acid lubricant to the lower non-magnetic layer as well, so that the magnetic layer and the magnetic layer surface contain a sufficient lubricant. However, if a fatty acid is added to the lower non-magnetic layer, the fatty acid added firmly adheres to the non-magnetic powder surface and cannot exhibit a sufficiently lubrication in the magnetic layer and the magnetic layer surface as is expected. Moreover, in the double paint type magnetic recording medium, there can be seen a phenomenon that the lubricant added to the magnetic layer is pulled into the lower non-magnetic powder, making it difficult to assure the tape running durability.